A tape player such as a video tape recorder (referred as VTR hereafter) or an audio tape recorder typically includes a tape position data indicator. The tape position data indicator indicates data corresponding to a tape position of the tape wound on a supply reel or a take-up reel of a cassette tape. The data corresponding to the tape position will be referred as the tape position data hereafter.
The tape position data represents either one of a remaining tape length wound yet on the supply reel, a past tape length wound already on the take-up reel, a remaining tape play time corresponding to the remaining tape length, a past tape play time corresponding to the past tape length or ratios such as percentages of the tape lengths or the tape play times. The tape position data can be obtained by measuring a volume of tape wound on the supply reel or the take-up reel. The tape volume is obtained by measuring, for example, the diameter of the tape part wound on the reel.
Referring now to FIG. 1, a typical calculation for obtaining the tape position data will be described. FIG. 1 diagrammatically shows a content of cassette tapes. As shown in FIG. 1, a tape 10 is wound between a supply reel 11 and a take-up reel 12 of the cassette tape. Here it is assumed that reel hubs 11a and 12a of the supply reel 11 and the take-up reel 12 have a same diameter D, a tape part 10s on the supply reel 11 is wound at a radius Rs and another tape part 10t on the take-up reel 12 is wound at a radius Rt. Then, following relations are established. ##EQU1## wherein Ns is winding turns of the tape part 10s wound on the supply reel 11, Nt is winding turns of the tape part 10t wound on the take-up reel 12 and Th is a thickness of the tape 10.
Tape lengths Ls and Lt of the tape parts 10s and 10t are obtained as follows: ##EQU2##
The tape winding turns Ns and Nt of the tape parts 10s and 10t are obtained from Equations (3) and (4) as follows: ##EQU3##
Generally, a tape speed V of the tape 10 running from the supply reel 11 to the take-up reel 12 is given by differentiating the length L of the tape 10 with respect to a time t. That is, the tape speed V is given as a differential equation of V=dL/dt. Rotation periods Ps and Pt of the supply reel 11 and the take-up reel 12 are obtained from a reciprocal of the tape speed V. Thus, the rotation periods Ps and Pt are obtained as follows: ##EQU4##
The tape lengths Ls and Lt of the tape parts 10s and 10t wound on the supply reel 11 and the take-up reel 12 are obtained from Equations (7) and (8) as follows: ##EQU5##
The thickness Th of the tape 10 and the diameter D of the reel hubs are defined by every type of cassette tapes, e.g., T-30 type cassette tape, T-60 type cassette tape, T-120 type cassette tape, etc. Accordingly, the tape lengths Ls and Lt of the tape parts 10s and 10t wound on the supply reel 11 and the take-up reel 12 can be calculated by measuring the rotation periods Ps and Pt, provided that the data designating the type of the cassette tape are set in the tape player and the tape speed V are previously known.
The tape lengths Ls, Lt of the tape part 10s, 10t wound on the reels 11, 12 are obtained by calculations of Equation (9), (10), as described above.
Conventionally, the above calculations of Equation (9), (10) are carried out by a microcomputor. Data associated with the cassette tape type, i.e., data designating the reel hub diameter D and the tape thickness Th and a data associated with the tape speed mode, i.e., a data designating the tape speed V are previously stored in a memory such as a ROM (Read Only Memory) associated to the microcomputor. The tape speed modes include a normal speed mode, a fast speed mode, a slow speed mode, etc.
The microcomputor is required to have a large scale of capacity for calculation of quadratic equations such as Equations (5), (6). Furthermore, in typical tape players, the microcomputor carries out not only the calculation of tape position, but also other operations for controlling the tape player. Then the capacity scale of the microcomputor increases more and more. Or varieties of the cassette tape types and the tape speed modes available for the calculation of the tape position are restricted.